1. Field of the Invention
The present invention relates to a main steam pressure disturbance preventing apparatus of a nuclear power plant which is so constructed as to be able to prevent pressure disturbance produced due to the disturbance of the liquid level of a pressure detection pipe or a water level detector generated when hydrogen and oxygen contained in vapor generated as a result of radiolysis of core cooling water in a main steam system or a drain system at a nuclear power plant are dissolved into liquid phase of the pressure detection pipe or the water level detector and the dissolved gas is evaporated due to the decrease of the process pressure, and thus, maintain pressure and water level measurements in the satisfactory state.
2. Description of the Related Art
At a boiling water reactor power plant, a main steam pipe is connected to a reactor pressure vessel in order to lead steam generated in a reactor core directly to a turbine. Assuming the possible break of the main steam pipe, main steam separation valves are provided at the inside and the outside of a reactor container, respectively to form a reactor coolant pressure boundary.
The outline of the main steam system and the drain system of a boiling water reactor power plant will be briefly explained referring to FIG. 10. Steam generated in a reactor 1 is sent to a steam turbine 3 by passing through a main steam pipe 2 of the main steam system along with hydrogen and oxygen produced as a result of the radiolysis. Part of the steam worked in steam turbine 3 is sent to a feed-water heater 5 by passing through a turbine bleeding pipe 4.
On the other hand, the remainder of the steam worked in steam turbine 3 is condensed in a condenser 6, boosted by a feed-water pump 7 and sent to feed-water heater 5. In this feed-water heater 5, feed-water from feed-water pump 7 is heated by the steam worked in steam turbine 3, and this heated feed-water is sent to reactor 1 by passing through a feed-water pipe 9.
The steam that was heat exchanged in feed-water heater 5 is condensed to drain and recovered by condenser 6 after passing through a drain pipe 8 of the drain system. As the steam generated in reactor 1 is accompanied with hydrogen and oxygen produced as a result of the radiolysis, hydrogen and oxygen exist in the small amount in the main steam system and the drain system, as described above.
For measuring pressure in main steam pipe 2 of the main steam system, as shown in FIG. 11, a detection pipe 10 is connected to a pressure detection seat (not shown) of main steam pipe 2, and a main instrumentation valve 11 and an upward detection pipe 12 are connected to detection pipe 10 and a pressure detector 13 is connected to detection pipe 10 at the downstream side. Here, as hydrogen and oxygen exist in main steam pipe 2 as described above, hydrogen and oxygen having lower specific gravity than steam may possibly be accumulated in upward detection pipe 12.
In detection pipe 10, water is filled so as to give a prescribed hydrostatic head to pressure detector 13. Accumulated hydrogen and oxygen are dissolved into the liquid phase of detection pipe 10. When the process side pressure is decreased, the hydrogen and oxygen dissolved in the liquid phase of detection pipe 10 are boiled under the reduced pressure. The hydrostatic head applied to pressure detector 13 is changed due to the disturbance of the liquid phase of detection pipe 10 by the boiling under the reduced pressure. The thus caused disturbance of the liquid level appears as the disturbance to the output signal of pressure detector 13. As a result of this disturbance, there are such problems that the supervision and control of the nuclear power plant are adversely affected.